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<div class="title">samples/cpp/tutorial_code/ImgTrans/houghlines.cpp</div>  </div>
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<p>An example using the Hough line detector </p><div class="image">
<img src="../../Hough_Lines_Tutorial_Original_Image.jpg" alt="Hough_Lines_Tutorial_Original_Image.jpg"/>
<div class="caption">
Sample input image</div></div>
 <div class="image">
<img src="../../Hough_Lines_Tutorial_Result.jpg" alt="Hough_Lines_Tutorial_Result.jpg"/>
<div class="caption">
Output image</div></div>
 <div class="fragment"><div class="line"></div><div class="line"><span class="preprocessor">#include &quot;<a class="code" href="../../d6/d87/imgcodecs_8hpp.html">opencv2/imgcodecs.hpp</a>&quot;</span></div><div class="line"><span class="preprocessor">#include &quot;<a class="code" href="../../d4/dd5/highgui_8hpp.html">opencv2/highgui.hpp</a>&quot;</span></div><div class="line"><span class="preprocessor">#include &quot;<a class="code" href="../../d1/d4f/imgproc_2include_2opencv2_2imgproc_8hpp.html">opencv2/imgproc.hpp</a>&quot;</span></div><div class="line"></div><div class="line"><span class="keyword">using namespace </span><a class="code" href="../../d2/d75/namespacecv.html">cv</a>;</div><div class="line"><span class="keyword">using namespace </span><a class="code" href="../../d8/dcc/namespacestd.html">std</a>;</div><div class="line"></div><div class="line"><span class="keywordtype">int</span> main(<span class="keywordtype">int</span> argc, <span class="keywordtype">char</span>** argv)</div><div class="line">{</div><div class="line">    <span class="comment">// Declare the output variables</span></div><div class="line">    <a name="_a0"></a><a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a> dst, cdst, cdstP;</div><div class="line"></div><div class="line">    <span class="keyword">const</span> <span class="keywordtype">char</span>* default_file = <span class="stringliteral">&quot;sudoku.png&quot;</span>;</div><div class="line">    <span class="keyword">const</span> <span class="keywordtype">char</span>* filename = argc &gt;=2 ? argv[1] : default_file;</div><div class="line"></div><div class="line">    <span class="comment">// Loads an image</span></div><div class="line">    <a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a> src = <a name="a1"></a><a class="code" href="../../d4/da8/group__imgcodecs.html#ga288b8b3da0892bd651fce07b3bbd3a56">imread</a>( <a name="a2"></a><a class="code" href="../../d6/dba/group__core__utils__samples.html#ga3a33b00033b46c698ff6340d95569c13">samples::findFile</a>( filename ), <a name="a3"></a><a class="code" href="../../d8/d6a/group__imgcodecs__flags.html#gga61d9b0126a3e57d9277ac48327799c80ae29981cfc153d3b0cef5c0daeedd2125">IMREAD_GRAYSCALE</a> );</div><div class="line"></div><div class="line">    <span class="comment">// Check if image is loaded fine</span></div><div class="line">    <span class="keywordflow">if</span>(src.<a name="a4"></a><a class="code" href="../../d3/d63/classcv_1_1Mat.html#abbec3525a852e77998aba034813fded4">empty</a>()){</div><div class="line">        printf(<span class="stringliteral">&quot; Error opening image\n&quot;</span>);</div><div class="line">        printf(<span class="stringliteral">&quot; Program Arguments: [image_name -- default %s] \n&quot;</span>, default_file);</div><div class="line">        <span class="keywordflow">return</span> -1;</div><div class="line">    }</div><div class="line"></div><div class="line">    <span class="comment">// Edge detection</span></div><div class="line">    <a name="a5"></a><a class="code" href="../../dd/d1a/group__imgproc__feature.html#ga04723e007ed888ddf11d9ba04e2232de">Canny</a>(src, dst, 50, 200, 3);</div><div class="line"></div><div class="line">    <span class="comment">// Copy edges to the images that will display the results in BGR</span></div><div class="line">    <a name="a6"></a><a class="code" href="../../d8/d01/group__imgproc__color__conversions.html#ga397ae87e1288a81d2363b61574eb8cab">cvtColor</a>(dst, cdst, <a name="a7"></a><a class="code" href="../../d8/d01/group__imgproc__color__conversions.html#gga4e0972be5de079fed4e3a10e24ef5ef0a869da65c045477f2f17d39395df65b2d">COLOR_GRAY2BGR</a>);</div><div class="line">    cdstP = cdst.<a name="a8"></a><a class="code" href="../../d3/d63/classcv_1_1Mat.html#adff2ea98da45eae0833e73582dd4a660">clone</a>();</div><div class="line"></div><div class="line">    <span class="comment">// Standard Hough Line Transform</span></div><div class="line">    vector&lt;Vec2f&gt; lines; <span class="comment">// will hold the results of the detection</span></div><div class="line">    <a name="a9"></a><a class="code" href="../../dd/d1a/group__imgproc__feature.html#ga46b4e588934f6c8dfd509cc6e0e4545a">HoughLines</a>(dst, lines, 1, <a name="a10"></a><a class="code" href="../../db/de0/group__core__utils.html#ga677b89fae9308b340ddaebf0dba8455f">CV_PI</a>/180, 150, 0, 0 ); <span class="comment">// runs the actual detection</span></div><div class="line"><span class="comment"></span>    <span class="comment">// Draw the lines</span></div><div class="line">    <span class="keywordflow">for</span>( <span class="keywordtype">size_t</span> i = 0; i &lt; lines.size(); i++ )</div><div class="line">    {</div><div class="line">        <span class="keywordtype">float</span> rho = lines[i][0], theta = lines[i][1];</div><div class="line">        <a name="_a11"></a><a class="code" href="../../db/d4e/classcv_1_1Point__.html">Point</a> pt1, pt2;</div><div class="line">        <span class="keywordtype">double</span> a = <a name="a12"></a><a class="code" href="../../d0/de1/group__core.html#gaf0f2fe47183d063fb7415097fbadb570">cos</a>(theta), b = <a name="a13"></a><a class="code" href="../../d0/de1/group__core.html#ga53a8656033a51db64caa72ee9d4e93b4">sin</a>(theta);</div><div class="line">        <span class="keywordtype">double</span> x0 = a*rho, y0 = b*rho;</div><div class="line">        pt1.<a name="a14"></a><a class="code" href="../../db/d4e/classcv_1_1Point__.html#a4c96fa7bdbfe390be5ed356edb274ff3">x</a> = <a name="a15"></a><a class="code" href="../../db/de0/group__core__utils.html#ga085eca238176984a0b72df2818598d85">cvRound</a>(x0 + 1000*(-b));</div><div class="line">        pt1.<a name="a16"></a><a class="code" href="../../db/d4e/classcv_1_1Point__.html#a157337197338ff199e5df1a393022f15">y</a> = <a class="code" href="../../db/de0/group__core__utils.html#ga085eca238176984a0b72df2818598d85">cvRound</a>(y0 + 1000*(a));</div><div class="line">        pt2.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a4c96fa7bdbfe390be5ed356edb274ff3">x</a> = <a class="code" href="../../db/de0/group__core__utils.html#ga085eca238176984a0b72df2818598d85">cvRound</a>(x0 - 1000*(-b));</div><div class="line">        pt2.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a157337197338ff199e5df1a393022f15">y</a> = <a class="code" href="../../db/de0/group__core__utils.html#ga085eca238176984a0b72df2818598d85">cvRound</a>(y0 - 1000*(a));</div><div class="line">        <a name="a17"></a><a class="code" href="../../d6/d6e/group__imgproc__draw.html#ga7078a9fae8c7e7d13d24dac2520ae4a2">line</a>( cdst, pt1, pt2, <a name="a18"></a><a class="code" href="../../dc/d84/group__core__basic.html#ga599fe92e910c027be274233eccad7beb">Scalar</a>(0,0,255), 3, <a name="a19"></a><a class="code" href="../../d6/d6e/group__imgproc__draw.html#ggaf076ef45de481ac96e0ab3dc2c29a777a85fdabe5335c9e6656563dfd7c94fb4f">LINE_AA</a>);</div><div class="line">    }</div><div class="line"></div><div class="line">    <span class="comment">// Probabilistic Line Transform</span></div><div class="line">    vector&lt;Vec4i&gt; linesP; <span class="comment">// will hold the results of the detection</span></div><div class="line">    <a name="a20"></a><a class="code" href="../../dd/d1a/group__imgproc__feature.html#ga8618180a5948286384e3b7ca02f6feeb">HoughLinesP</a>(dst, linesP, 1, <a class="code" href="../../db/de0/group__core__utils.html#ga677b89fae9308b340ddaebf0dba8455f">CV_PI</a>/180, 50, 50, 10 ); <span class="comment">// runs the actual detection</span></div><div class="line"><span class="comment"></span>    <span class="comment">// Draw the lines</span></div><div class="line">    <span class="keywordflow">for</span>( <span class="keywordtype">size_t</span> i = 0; i &lt; linesP.size(); i++ )</div><div class="line">    {</div><div class="line">        <a name="_a21"></a><a class="code" href="../../d6/dcf/classcv_1_1Vec.html">Vec4i</a> l = linesP[i];</div><div class="line">        <a class="code" href="../../d6/d6e/group__imgproc__draw.html#ga7078a9fae8c7e7d13d24dac2520ae4a2">line</a>( cdstP, <a name="a22"></a><a class="code" href="../../dc/d84/group__core__basic.html#ga1e83eafb2d26b3c93f09e8338bcab192">Point</a>(l[0], l[1]), <a class="code" href="../../dc/d84/group__core__basic.html#ga1e83eafb2d26b3c93f09e8338bcab192">Point</a>(l[2], l[3]), <a class="code" href="../../dc/d84/group__core__basic.html#ga599fe92e910c027be274233eccad7beb">Scalar</a>(0,0,255), 3, <a class="code" href="../../d6/d6e/group__imgproc__draw.html#ggaf076ef45de481ac96e0ab3dc2c29a777a85fdabe5335c9e6656563dfd7c94fb4f">LINE_AA</a>);</div><div class="line">    }</div><div class="line"></div><div class="line">    <span class="comment">// Show results</span></div><div class="line">    <a name="a23"></a><a class="code" href="../../d7/dfc/group__highgui.html#ga453d42fe4cb60e5723281a89973ee563">imshow</a>(<span class="stringliteral">&quot;Source&quot;</span>, src);</div><div class="line">    <a class="code" href="../../d7/dfc/group__highgui.html#ga453d42fe4cb60e5723281a89973ee563">imshow</a>(<span class="stringliteral">&quot;Detected Lines (in red) - Standard Hough Line Transform&quot;</span>, cdst);</div><div class="line">    <a class="code" href="../../d7/dfc/group__highgui.html#ga453d42fe4cb60e5723281a89973ee563">imshow</a>(<span class="stringliteral">&quot;Detected Lines (in red) - Probabilistic Line Transform&quot;</span>, cdstP);</div><div class="line"></div><div class="line">    <span class="comment">// Wait and Exit</span></div><div class="line">    <a name="a24"></a><a class="code" href="../../d7/dfc/group__highgui.html#ga5628525ad33f52eab17feebcfba38bd7">waitKey</a>();</div><div class="line">    <span class="keywordflow">return</span> 0;</div><div class="line">}</div></div><!-- fragment --> </div><!-- contents -->
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